Since the invention of the integrated circuit, the semiconductor industry has continuously sought to improve the density of integrated circuit components (transistors, diodes, resistors, capacitors, etc.). For the most part, improvements in density have come from reductions in feature size, allowing more components to be formed within a given area. These improvements have been made while components remain in an essentially two-dimensional layout. Although dramatic increases in density have been realized within the limits of a two-dimensional layout, further improvements are difficult to achieve.
Three-dimensional integrated circuits (3D ICs) have been created to overcome these limitations. In a 3D IC, two or more semiconductor bodies, each including an integrated circuit, are formed, aligned vertically, and bonded together.